Metapneumovirus (MPV) is an enveloped non-segmented negative-strand RNA virus in the family Paramyxoviridae, genus Pneumovirus. It is a common cause of bronchiolitis and pneumonia among children and the elderly. MPV also causes repeated infections including severe lower respiratory tract disease, which may occur at any age, especially among the elderly or those with compromised cardiac, pulmonary, or immune systems. Current treatment includes administration of the anti-viral agent Ribaviran.
In nature, the MPV F protein is initially expressed as a single polypeptide precursor, designated F0. F0 trimerizes in the endoplasmic reticulum and is proteolytically processed at a conserved cleavage site, generating F1 and F2 polypeptides. Three protomers of the F2-F1 heterodimer assemble to form a mature trimeric F protein, which adopts a metastable prefusion conformation that can be triggered to undergo a conformational change that fuses the viral and target-cell membranes. Due to its obligatory role in MPV entry, the MPV F protein is the target of neutralizing antibodies and the subject of vaccine development; however, like other MPV antigens, prior efforts to develop an MPV F protein-based vaccine have proven unsuccessful.